Отказ от ответственности

namespace IconExUpdate
{
 using System;
 using System.Runtime.InteropServices;
 using System.Security;

 [SuppressUnmanagedCodeSecurity()]
 internal static class NativeMethods
 {
 [DllImport("kernel32")]
 internal static extern IntPtr BeginUpdateResource(string fileName, [MarshalAs(UnmanagedType.Bool)] bool deleteExistingResources);

 [DllImport("kernel32")]
 public static extern bool UpdateResource(IntPtr hUpdate, IntPtr type, IntPtr name, short language, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 5)] byte[] data, int dataSize);

 [DllImport("kernel32")]
 public static extern bool EndUpdateResource(IntPtr hUpdate, [MarshalAs(UnmanagedType.Bool)] bool discard);
 }
}

namespace IconExUpdate
{
 using System.Runtime.InteropServices;

 public static class Structures
 {
 #region For Icon Change
 [StructLayout(LayoutKind.Sequential)]
 public partial struct ICONDIR
 {
 public ushort Reserved;
 public ushort Type;
 public ushort Count;
 }

 [StructLayout(LayoutKind.Sequential)]
 public partial struct ICONDIRENTRY
 {
 public byte Width;
 public byte Height;
 public byte ColorCount;
 public byte Reserved;
 public ushort Planes;
 public ushort BitCount;
 public int BytesInRes;
 public int ImageOffset;
 }

 [StructLayout(LayoutKind.Sequential)]
 public partial struct BITMAPINFOHEADER
 {
 public uint Size;
 public int Width;
 public int Height;
 public ushort Planes;
 public ushort BitCount;
 public uint Compression;
 public uint SizeImage;
 public int XPelsPerMeter;
 public int YPelsPerMeter;
 public uint ClrUsed;
 public uint ClrImportant;
 }

 [StructLayout(LayoutKind.Sequential, Pack = 2)]
 public partial struct GRPICONDIRENTRY
 {
 public byte Width;
 public byte Height;
 public byte ColorCount;
 public byte Reserved;
 public ushort Planes;
 public ushort BitCount;
 public int BytesInRes;
 public ushort ID;
 }
 #endregion
 }
}

namespace IconExUpdate
{
 using System;
 using System.IO;
 using System.Runtime.InteropServices;

 public class IconChanger
 {
 public void InjectIcon(string exeFileName, string iconFileName)
 {
 InjectIcon(exeFileName, iconFileName, 1, 1);
 }

 public void InjectIcon(string exeFileName, string iconFileName, uint iconGroupID, uint iconBaseID)
 {
 const uint RT_ICON = 3, RT_GROUP_ICON = 14;
 var iconFile = FromFile(iconFileName);
 var hUpdate = NativeMethods.BeginUpdateResource(exeFileName, false);
 var data = iconFile.CreateIconGroupData(iconBaseID);
 NativeMethods.UpdateResource(hUpdate, new IntPtr(RT_GROUP_ICON), new IntPtr(iconGroupID), 0, data, data.Length);
 for (int i = 0, loopTo = iconFile.ImageCount - 1; i <= loopTo; i++)
 {
 var image = iconFile.Get_ImageData(i);
 NativeMethods.UpdateResource(hUpdate, new IntPtr(RT_ICON), new IntPtr(iconBaseID + i), 0, image, image.Length);
 }
 NativeMethods.EndUpdateResource(hUpdate, false);
 }

 private Structures.ICONDIR iconDir = new Structures.ICONDIR();
 private Structures.ICONDIRENTRY[] iconEntry;
 private byte[][] iconImage;

 public int ImageCount => iconDir.Count;
 public byte[] Get_ImageData(int index) => iconImage[index];

 public static IconChanger FromFile(string filename)
 {
 var instance = new IconChanger();
 try
 {
 byte[] fileBytes = File.ReadAllBytes(filename);
 var pinnedBytes = GCHandle.Alloc(fileBytes, GCHandleType.Pinned);
 instance.iconDir = (Structures.ICONDIR)Marshal.PtrToStructure(pinnedBytes.AddrOfPinnedObject(), typeof(Structures.ICONDIR));
 instance.iconEntry = new Structures.ICONDIRENTRY[instance.iconDir.Count];
 instance.iconImage = new byte[instance.iconDir.Count][];
 int offset = Marshal.SizeOf(instance.iconDir);
 Type iconDirEntryType = typeof(Structures.ICONDIRENTRY);
 int size = Marshal.SizeOf(iconDirEntryType);
 for (int i = 0, loopTo = instance.iconDir.Count - 1; i <= loopTo; i++)
 {
 Structures.ICONDIRENTRY entry = (Structures.ICONDIRENTRY)Marshal.PtrToStructure(new IntPtr(pinnedBytes.AddrOfPinnedObject().ToInt64() + offset), iconDirEntryType);
 instance.iconEntry[i] = entry;
 instance.iconImage[i] = new byte[entry.BytesInRes];
 Buffer.BlockCopy(fileBytes, entry.ImageOffset, instance.iconImage[i], 0, entry.BytesInRes);
 offset += size;
 }

 pinnedBytes.Free();
 }
 catch { }
 return instance;
 }

 public byte[] CreateIconGroupData(uint iconBaseID)
 {
 try
 {
 int sizeOfIconGroupData = Marshal.SizeOf(typeof(Structures.ICONDIR)) + (Marshal.SizeOf(typeof(Structures.GRPICONDIRENTRY)) * ImageCount);
 var data = new byte[sizeOfIconGroupData];
 var pinnedData = GCHandle.Alloc(data, GCHandleType.Pinned);
 Marshal.StructureToPtr(iconDir, pinnedData.AddrOfPinnedObject(), false);
 int offset = Marshal.SizeOf(iconDir);
 for (int i = 0, loopTo = ImageCount - 1; i <= loopTo; i++)
 {
 var grpEntry = new Structures.GRPICONDIRENTRY();
 var bitmapheader = new Structures.BITMAPINFOHEADER();
 var pinnedBitmapInfoHeader = GCHandle.Alloc(bitmapheader, GCHandleType.Pinned);
 Marshal.Copy(Get_ImageData(i), 0, pinnedBitmapInfoHeader.AddrOfPinnedObject(), Marshal.SizeOf(typeof(Structures.BITMAPINFOHEADER)));
 pinnedBitmapInfoHeader.Free();
 grpEntry.Width = iconEntry[i].Width;
 grpEntry.Height = iconEntry[i].Height;
 grpEntry.ColorCount = iconEntry[i].ColorCount;
 grpEntry.Reserved = iconEntry[i].Reserved;
 grpEntry.Planes = bitmapheader.Planes;
 grpEntry.BitCount = bitmapheader.BitCount;
 grpEntry.BytesInRes = iconEntry[i].BytesInRes;
 ushort result = unchecked((ushort)(iconBaseID + i));
 grpEntry.ID = result;
 Marshal.StructureToPtr(grpEntry, new IntPtr(pinnedData.AddrOfPinnedObject().ToInt64() + offset), false);
 offset += Marshal.SizeOf(typeof(Structures.GRPICONDIRENTRY));
 }

 pinnedData.Free();
 return data;
 }
 catch
 {
 return null;
 }
 }
 }
}

string IconPath = string.Empty; // Переменная где будет путь к иконки
// Добавляем иконку
using var OpenFileDialog = new OpenFileDialog
{
 Filter = "Icon Files (*.ico)|*.ico",
 FilterIndex = 1,
 InitialDirectory = Environment.CurrentDirectory,
 RestoreDirectory = true
};
if (OpenFileDialog.ShowDialog() == DialogResult.OK)
{
 IconPath = OpenFileDialog.FileName; // Присваиваем переменную к нашему пути до иконки
}
if (!string.IsNullOrEmpty(IconPath)) // Если путь к иконке не пустой
{
 var ico = new IconChanger(); // Создаём экземпляр класса.
 ico.InjectIcon(outfilePath, IconPath); // Заменяем иконку.
}